Preparation And Properties Of Manganese Oxide And Molybdenum Oxide Composite Electrode Materials

In recent years,due to oil shortage and environmental pollution,the development of efficient energy storage system has become a hot topic of international research.Supercapacitors and lithium-ion batteries have the advantages of long cycle life,environmental friendliness,green non-pollution and other traditional energy storage devices.They are new energy storage devices and become potential energy storage systems for electronic communications,mobile devices,new energy vehicles and so on.The research and development of related electrode materials is the key factor to improve the performance of high efficiency storage system.Manganese oxide and molybdenum oxide have attracted much attention due to their high theoretical capacity in many electrode materials.In this paper,two kinds of materials were modified by simple solvothermal method and in-situ reduction synthesis method focusing on their own shortcomings,such as poor conductivity,poor cyclic stability and so on.The surface morphology,structure and surface oxygen-containing functional groups of the samples were analyzed by SEM,TEM,XRD and XPS.The electrochemical performance of the synthesized composite electrode material was tested in a three-electrode test system and a blue electric test system.First of all,a one-dimensional hierarchical Ag nanoparticle?AgNP?/MnO₂nanorod?MND?nanocomposite was synthesized by combining a simple solvothermal method and a facile reduction approach in situ.Owing to its high electrical conductivity,the resulting AgNP/MND nanocomposite displayed a high specific capacitance of 314 F·g^-1 at a current density of 2 A g^-1,which was much higher than that of pure MNDs(178 F·g^-1).Resistances of the electrolyte?R_s?and charge transportation(R_ct)of the nanocomposite were much lower than that of pure MNDs.Moreover,the nanocomposite exhibited outstanding long-term cycling ability?only 9%loss of initial capacity after 1 000 cycles?.Secondly,on the basis of AgNP/MND nanocomposites,Ag nanoparticles modified carbon coated MnO₂ nanorods?MCA?were prepared.The MCA-1.5 sample exhibited the highest specific capacitance of 628 F·g^-1 at the current density of 1A·g^-1 in three electrode systems.Particularly,a fabricated asymmetric supercapacitor,using MCA-1.5 and active carbon as the positive and negative electrodes,respectively,delivered a maximum energy density of 48.3 W·h·kg^-1 at power density of 851.7W·kg^-1 and exhibited a superior,long cycle life,showing?98.5%specific capacitance retention after 2 000 cycles.Two series of such devices can light up the LED bulb,proving the actual energy storage applicability of the device.Thirdly,PAN nanofibers are selected as flexible supports for MoO₂/MoS₂hybrids active materia,and the MoS₂ nanostructures are grown into the MoO₂ layer via an in-situ conversion reaction.The sample PMOS-0.5 exhibits the highest specific capacitance of 439 F·g^-1 at the current density of 1 A·g^-1 in three electrode systems.Particularly,the as-fabricated asymmetric device using PMOS-0.5 as the positive electrode and active carbon as the negative electrode delivers a maximum energy density of 46 Wh·kg^-1 at power density of 2246.9 W·kg^-1.The materials are used to construct a solid-state asymmetric SC?ASC?,the device could light up a LED belt.Moreover,there is no significant change in the brightness and duration of the LED lamp before and after the device bends into a ring when using solid electrolyte,indicating that the material has perfect flexibility and stability.In addition,the electrode material also exhibited good cycle performance,and the specific capacitance remained at about 98.9%after 2 000 cycles.Finally,in situ synthesis method was used to synthesize MoS₂ with thiourea and MoO₂ as S source and Mo source,respectively.MoS₂ nanostructure was grown in the bulk phase of MoO₂ particles.CNFs/MoO₂/MoS₂ composite electrode material was synthesized on carbon nanofibers?CNFs?.The prepared CNFs/MoO₂/MoS₂ ternary nanostructured materials not only have a highly reversible Li⁺storage capacity due to the synergistic effect between the three components,but also exhibit excellent rate performance and cycle stability.The discharge capacity of the lithium ion battery prepared by using the composite material as the electrode in the first two tests was987 mAh·g^-1 and 966 mAh·g^-1,respectively,and the corresponding coulombic efficiencies were 97.5%and 98%.